Tehran University of Medical Sciences Frontiers in Dentistry 2676-296X 16 3 2019 01 30 187 193 EN Mehdi Rostami Rad Department of Microbiology, School of Medicine, Tehran University of Medical Sciences, Tehran, Iran Maryam Pourhajibagher Dental Research Center, Dentistry Research Institute, Tehran University of Medical Sciences, Tehran, Iran Amir Reza Rokn Dental Implant Research Center, Dentistry Research Institute, Tehran University of Medical Sciences, Tehran, Iran Hamid Reza Barikani Dental Implant Research Center, Dentistry Research Institute, Tehran University of Medical Sciences, Tehran, Iran Abbas Bahador Department of Microbiology, School of Medicine, Tehran University of Medical Sciences, Tehran, Iran 2018 08 01 2019 01 07 Objectives: Eradication of Aggregatibacter actinomycetemcomitans (A. action-mycetemcomitans), as an opportunistic periodontopathogen, and inhibition of its virulence factor expression require a new adjunctive therapeutic method. In this study, we accessed the expression level of rcpA gene, as a virulence factor associated with A. actinomycetemcomitans biofilm formation, following treatment by antimicrobial photodynamic therapy (aPDT) using indocyanine green (ICG) doped with chitosan nanoparticles (CS-NPs@ICG). Materials and Methods: CS-NPs@ICG was synthesized and examined using scanning electron microscopy (SEM). A. actinomycetemcomitans ATCC 33384 strain was treated with CS-NPs@ICG, as a photosensitizer, which was excited with a diode laser at the wavelength of 810 nm with the energy density of 31.2 J/cm2. Quantitative real-time polymerase chain reaction (qRT-PCR) was performed to determine the changes in rcpA gene expression level. Results: Synthetized CS-NPs@ICG was confirmed via SEM. The results revealed that CS-NPs@ICG-mediated aPDT could significantly decrease rcpA gene expression to 13.2-fold (P<0.05). There was a remarkable difference between aPDT using CS-NPs@ICG and ICG (P<0.05). The diode laser, ICG, and CS-NPs@ICG were unable to significantly downregulate rcpA gene expression (P>0.05). Conclusion: aPDT with CS-NPs@ICG leads to a decrease of the virulence factor of A. actinomycetemcomitans and can be used as an adjunct to routine treatments for successful periodontal therapy in vivo. https://fid.tums.ac.ir/index.php/fid/article/view/2752 https://fid.tums.ac.ir/index.php/fid/article/download/2752/1757